1. Field of the Invention
This invention relates generally to determining analyte concentrations within living tissue.
2. Description of the Related Art
Millions of diabetics are forced to draw blood on a daily basis to determine their blood glucose levels. A search for a non-invasive methodology to accurately determine blood glucose levels has been substantially expanded in order to alleviate the discomfort of these individuals.
A significant advance in the state of the art of non-invasive blood glucose analysis has been realized by an apparatus taught in U.S. Pat. No. 6,198,949, titled SOLID-STATE NON-INVASIVE INFRARED ABSORPTION SPECTROMETER FOR THE GENERATION AND CAPTURE OF THERMAL GRADIENT SPECTRA FROM LIVING TISSUE, issued Mar. 6, 2001; and by methodology taught in U.S. Pat. No. 6,161,028, titled METHOD FOR DETERMINING ANALYTE CONCENTRATION USING PERIODIC TEMPERATURE MODULATION AND PHASE DETECTION, issued Dec. 12, 2000; and in the Assignee""s U.S. patent application Ser. No. 09/538,164, titled METHOD AND APPARATUS FOR DETERMINING ANALYTE CONCENTRATION USING PHASE AND MAGNITUDE DETECTION OF A RADIATION TRANSFER FUNCTION. Additional information relating to calibration of such non-invasive blood analysis is taught in U.S. Pat. No. 6,049,081, titled SUBSURFACE THERMAL GRADIENT SPECTROMETRY, issued Apr. 11, 2000; and by U.S. Pat. No. 6,196,046 B1, titled DEVICES AND METHODS FOR CALIBRATION OF A THERMAL GRADIENT SPECTROMETER, issued Mar. 6, 2001. The entire disclosure of all of the above mentioned patents and patent applications are hereby incorporated by reference herein and made a part of this specification.
U.S. Pat. No. 6,198,949 discloses a spectrometer for non-invasive measurement of thermal gradient spectra from living tissue. The spectrometer includes an infrared transmissive thermal mass, referred to as a thermal mass window, for inducing a transient temperature gradient in the tissue by means of conductive heat transfer with the tissue, and a cooling system in operative combination with the thermal mass for the cooling thereof. Also provided is an infrared sensor for detecting infrared emissions from the tissue as the transient temperature gradient progresses into the tissue, and for providing output signals proportional to the detected infrared emissions. A data capture system is provided for sampling the output signals received from the infrared sensor as the transient temperature gradient progresses into to the tissue. The transient thermal gradients arising due to the intermittent heating and cooling of the patient""s skin generate thermal spectra which yield very good measurements of the patient""s blood glucose levels.
Although the apparatus taught in the above-mentioned U.S. Pat. No. 6,198,949 has led to a significant advance in the state of the art of non-invasive blood glucose analysis, one possible source of error in such analysis arises due to physiological variation across the patient population. This variation, as well as other factors, can introduce systematic error into the measurements being performed.
In accordance with one embodiment, there is provided a method for calibrating a monitor comprising a non-invasive blood constituent monitor connected to a traditional measurement system via a data link. An amount of whole blood is withdrawn from a patient. A blood constituent in the amount of whole blood is analyzed with the traditional measurement system. A traditional monitor output representing a property of the blood constituent is generated. The thermal gradient inducing element of the non-invasive blood constituent monitor is placed in contact with a portion of the skin of the patient. The blood constituent in blood within the patient is analyzed by detecting thermal radiation at selected wavelengths. A non-invasive monitor output representing the property of the blood constituent is generated. The traditional monitor output and the non-invasive monitor output are compared to estimate an amount of error. The non-invasive monitor output is corrected based on the error.
In accordance with another embodiment, there is provided a blood constituent monitor that comprises a non-invasive blood constituent monitor that includes a thermal gradient inducing element. The non-invasive blood constituent monitor also includes an analyzer window. The blood constituent monitor also comprises a traditional measurement system that has a whole blood withdrawal portion and an analysis portion. The blood constituent monitor also comprises a data link that transfers data between the noninvasive blood constituent monitor and the traditional measurement system. The noninvasive blood constituent monitor and the traditional measurement system are permanently connected.
In accordance with another embodiment, there is provided a method for calibrating a non-invasive blood constituent monitor connected to a traditional measurement system via a data link. The operator determines whether there is a restricted period in effect. An on-site or an off-site measurement location is selected based on whether the restricted period is in effect. A traditional measurement of a blood constituent is performed at the selected measurement location using the traditional measurement system. A traditional monitor output representing a property of the blood constituent is generated. The analyzer window of the non-invasive blood constituent monitor is placed in contact with the skin of the patient. The blood constituent is analyzed with the non-invasive blood constituent monitor. A non-invasive monitor output representing the property of the blood constituent is generated. The traditional monitor output and the non-invasive monitor output are compared to estimate an error. The non-invasive monitor output is corrected based on the error.
In accordance with another embodiment, there is provided a blood constituent monitor that comprises a traditional measurement system configured to withdraw an amount of whole blood from a patient. The blood constituent monitor is also configured to analyze a blood constituent in the amount of whole blood to generate a traditional monitor output representing a property of the blood constituent. The blood constituent monitor also comprises a non-invasive monitor that has a thermal gradient inducing element configured to be placed in contact with the skin of the patient. The non-invasive monitor is configured to analyze the blood constituent in the patient to produce a non-invasive monitor output by detecting thermal radiation emitted by the blood constituent. The blood constituent monitor also comprises a data link connected to the traditional measurement system and connected to the non-invasive monitor. The data link is configured to transmit the output of the traditional measurement to the non-invasive monitor. The blood constituent monitor is configured to compare the traditional monitor output and the non-invasive monitor output.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.